@node dup, io
@subheading Syntax

@example
#include <unistd.h>

int dup(int old_handle);
@end example

@subheading Description

This function duplicates the given file handle.  Both handles refer to
the same file and file pointer. 

@subheading Return Value

The new file handle, or -1 if error.

@subheading Portability

@portability !ansi, posix

@subheading Example

@example
do_file(dup(fileno(stdin)));
@end example